When the widget Upcoming Events is activated some event concepts are displayed in the widget.
Widget settings: display dates, excerpt & thumbnail. Limit 5, lookahead 52 weeks and any category.
Event concept: Repeats each month on the 9th day at 10 o clock and the event is 2 hours long.
In that case the concept is shown in the widget.
Clicking the url in the widget shows a page not found, so thats okay.
When the concept is just on 1 day (no start or end date) it's not shown in the widget.
You can see the widget here in the sidebar on the right side.